Resistor network sets gain for fixed-gain differential amplifier

By adding an externalresistor network you can lower the gain of a fixed-gain differential amplifier (like the MAX9705) to the gain level required, but you must account for the loading effects of internal resistors. This note includes equations for calculating these effects, plus a link to a spreadsheet for selecting resistor values needed in the network.

When a fixed-gain amplifier does not offer the optimum gain for an application, you can adjust the gain to a lower value by adding an external resistor network. This attenuation circuit works like a voltage-divider, but with a key difference: the external network is loaded down by input resistors internal to the fixed-gain amplifier. For the differential-input configuration, this system can be reduced to an equivalent half circuit for analysis.